1. Field of Invention
This invention relates to the recovery of elemental sulfur and hydrogen from hydrogen sulfide generally contained in hydrocarbon fluids such as petroleum or natural gas. Further, the invention also relates to the removal and decomposition of H.sub.2 S from a natural gas stream via an electrochemical process.
2. State of the Art
Generally, hydrogen sulfide is removed from a hydrocarbon stream by solvent extraction followed by distillation. The separated H.sub.2 S gas is then converted to elemental sulfur by the widely used Claus process. The Claus process comprises a combustion stage, catalytic conversion stage, and tail gas clean up treatment. The process involves the following three reactions: EQU H.sub.2 S+3/2 O.sub.2 .fwdarw.SO.sub.2 +H.sub.2 O (1) Combustion Stage EQU 2H.sub.2 S+SO.sub.2 .fwdarw.S+2H.sub.2 O (2) Catalytic Stage EQU 3H.sub.2 S-3/2 O.sub.2 .fwdarw.S+3H.sub.2 O (3) Overall
Recently the National Chemical Laboratory for Industry in Japan, together with Idemitsu Kosan, announced development of a hybrid process which recovers both sulfur and hydrogen from hydrogen sulfide in hydrocarbon stream produced from oil refineries. The Idemitsu hybrid process involves two major operations. Initially, hydrogen sulfide is absorbed into a ferric chloride solution where a redox reaction occurs to convert H.sub.2 S and FeCl.sub.3 into sulfur, ferrous chloride and hydrochloric acid as follows: EQU H.sub.2 S(g)+2FeCl.sub.3 (aqueous).fwdarw.2FeCl.sub.2 +S(s)+2HCl(Aqueous)(4 )
After separation of sulfur through filtration, the solution of ferrous chloride (FeCI.sub.2) and hydrochloric acid (HCl) is electrolyzed to regenerate ferric chloride in the anodic chamber and produce hydrogen in the cathodic chamber as follows: EQU 2FeCl.sub.2 (Aq.)+2HCl (Aq.).fwdarw.2FeCl.sub.3 +H2(g). (Aq.)(5)
The overall reactions of (4) and (5) can be written as EQU H.sub.2 S(g).fwdarw.H.sub.2 (g)+S(s) (6)
Thus, the Idemitsu-hybrid process gives hydrogen as a byproduct which has chemical and fuel value and hence makes the process economically advantageous over the Claus process. The Idemitsu process is described in SRI international's document. (PEP Review No. 88-2-1).
However, both the above described processes involve several cumbersome steps to recover sulfur from hydrogen sulfide. In the Claus process, the reactions generate another hazardous chemical, SO.sub.2, as an intermediate product and also does not give hydrogen as a byproduct as the Idemitsu hybrid process does. In any event, both of these processes are expensive from energy and capital cost point of view.
Therefore, there is a need in the industry for an improved, one-step process for recovering sulfur from H.sub.2 S and preferably directly from natural gas and other petroleum products.